Methods for the production of a nonwoven fabric comprising melt spinning a thermoplastic resin and blowing it as fine fibers against a moving collecting plate have been known as the "melt-blowing process" (Japanese Patent Kokai (Early-Publication) Nos. 10,258/1974, 48,921/1974 and 121,570/1975, or "jet-spinning process" (Japanese Patent Publication Nos. 25,871/1969 and 26,977/1969).
Since in these known methods, a fiber stream is simply collected on a flat or hollow-cylindrical collecting plate having a large number of pores, they have the disadvantages that a part of the fiber stream blown onto a collecting plate tends to be scattered together with the blown gas, and that the thickness and weight per unit area of a nonwoven fabric collected on a plate are uneven. For example, in the production of a nonwoven fabric, particularly bulky, made of such fine fibers as having a fiber diameter of several microns, the scattering of fibers is so remarkable that the workability and operation environment tend to be deteriorated and that the resulting product is uneven. In order to prevent this phenomenon, there has been proposed a method comprising forcedly withdrawing the gas blown against the collecting plate by using a sucking means provided on the back side of the collecting plate. However, this method is disadvantageous in that it is uneconomical because of needing power for the exhaust of the gas, that the displacement of the sucking means has a limit, and further in that if the displacement is increased, a nonwoven fabric in contact with the surface of the collecting plate may also be sucked such that the density thereof is increased, resulting in difficulty in obtaining a uniform and bulky nonwoven fabric.
Furthermore, the prior art methods only produce nonwoven fabrics wherein fibers are disposed in parallel with the surface of the nonwoven fabrics, but cannot produce nonwoven fabrics wherein fibers are arranged in the vertical direction to the surface (i.e. in parallel with the thickness direction).
As a result of intensive studies on a method for producing a bulky and uniform nonwoven fabric consisting of fine fibers, the inventors have found that a bulky and uniform nonwoven fabric consisting of fine fibers can very easily be obtained by blowing a fiber stream of a thermoplastic resin into a valley-like space zone formed by two plates having a large number of holes, and that in particular, a nonwoven fabric wherein fibers are vertical to the surface of the nonwoven fabric (in parallel with the thickness direction) can be obtained by blowing a fiber stream into an area where the two porous plates meet. The present invention has been accomplished based on this finding.